Circuit arrangement for monitoring the state of charge of an accummulator

ABSTRACT

A circuit configuration for monitoring the state of charge of an accumulator battery, which is installed in particular in a motor vehicle, has a control unit that records and evaluates the flow of current out of or into the accumulator battery. The control unit is able to be shifted into a state with low current consumption (sleep mode), out of which it may be brought again by an activation signal. Moreover, a sensor is provided that emits a signal in response to a flow of current out of or into the accumulator battery.

FIELD OF THE INVENTION

The present invention relates to a circuit configuration for monitoringthe state of charge of an accumulator battery, which is disposed inparticular in a motor vehicle, having a control unit that records andevaluates the flow of current out of or into the accumulator battery.

BACKGROUND INFORMATION

A circuit configuration of this type is used, for example, in motorvehicles, to thereby continually have available the instantaneous stateof charge of the accumulator battery. By recording the accumulatorcurrent, the accumulator voltage and the accumulator temperature,relatively reliable information can be ascertained about the state ofthe accumulator battery. The indicated quantities are acquired and thestate of the accumulator battery is ascertained by the control unit.

Since the control unit is supplied with energy from the accumulatorbattery, when the engine is at rest and therefore electrical energy isnot being produced by the generator installed in a motor vehicle, thecontrol unit discharges the accumulator battery. To prevent this, thecontrol unit is switched off when the motor vehicle is in the reststate. As soon as the ignition is switched off and the currentconsumption in the motor vehicle has fallen sufficiently, the controlunit stores the instantaneous state of the accumulator battery and thenswitches itself off. The control unit is only switched on again when theignition is switched on.

Since, however, in today's motor vehicles there are frequently consumerswhich require energy even in the rest state of the motor vehicle, suchas, for example, an ice maker in the trunk of the motor vehicle, currentis drawn from the accumulator battery without this being registered bythe control unit. Because of this, the state of the accumulator batteryascertained by the control unit no longer agrees with the true state ofthe accumulator battery.

It may be that it is known from PCT International Patent Publication No.WO 99/50098 to shift a motor vehicle into a rest state (sleep mode) tothereby reduce the energy consumption; however, no indication can begathered from the cited document to monitor the state of charge of anaccumulator battery. The indicated publication deals with a monitoringsystem of a motor vehicle which has inputs for a plurality of vehiclesubsystems. To save on energy, the cited document proposes shifting themotor vehicle into a sleep mode, activation signals (wake-up signals)normally not being given to the inputs of the vehicle subsystems.

During the sleep mode, the inputs are permanently polled to therebydetect the appearance of a wake-up signal. If no wake-up signal appearsafter a certain time, the cycle time of the polling inputs is increased.If a wake-up signal still does not appear at the inputs after a furtherpredetermined time, the cycle time is increased once more. The intentionis to thereby reduce the energy consumption during the sleep mode.

Moreover, German Patent No. 41 23 811 A1 describes a method foroperating a microprocessor, in which the microprocessor may be switchedfrom an inactive to an active operating state by an activation signal atan interrupt input. After each entrance into the inactive state, theactivation signal is supplied to the interrupt input after a specifiabletime.

Furthermore, U.S. Pat. No. 4,965,550 describes a circuit configurationfor continually monitoring the status of a plurality of switches andso-called intelligent sensors (smart sensors), which are connected tothe switches. Each sensor is connected to a separate single point in asingle-wire bus, a smart-sensor multiplex configuration that representsa wake-up circuit acting on the sensor. The wake-up circuit permits theactivation of any switch of a group of switches having a high priority,in order to shift a microcontroller automatically from a waiting stateinto an active state. In the active state, all circuits of the entiresystem are supplied with energy, whereupon all switches and sensormodules are polled.

It is an object of the present invention to provide a circuitconfiguration of the type indicated at the outset in such a way thataccuracy in recording the state of charge of an accumulator battery isincreased.

SUMMARY OF THE INVENTION

According to the present invention, in a circuit configuration formonitoring the state of charge of an accumulator battery, which inparticular is installed in a motor vehicle and has a control unit thatrecords and evaluates the flow of current out of or into the accumulatorbattery, the control unit is able to be shifted into a state with lowcurrent consumption (sleep mode), out of which it may be brought againby an activation signal; and a sensor is provided which emits a signalin response to a flow of current out of or into the accumulator battery.

Because the control unit is able to be shifted into a state with lowcurrent consumption, the control unit may remain switched on permanentlywithout the state of charge of the accumulator battery therebynoticeably changing. Since the control unit is able to be brought out ofthe state with low current consumption again by an activation signal, itcan be shifted in a simple manner into the active state again. Due tothe sensor, which emits a signal in response to a flow of current out ofor into the accumulator battery, the control unit can thus always beeasily shifted into the active state when the state of charge of theaccumulator battery changes because of a flow of current out of or intothe accumulator battery.

Therefore, the circuit configuration of the present invention ensuresthat the control unit records a change in the charge state of theaccumulator battery at any time, without its being permanently in theactive state. Shifting the control unit into the state with low currentconsumption during the rest state of the motor vehicle advantageouslyprevents the charge state of the accumulator battery from changingnoticeably due to the draw of energy by the control unit. By the use ofa sensor that emits a signal in response to a flow of current in thelead of the accumulator battery, and because the control unit is broughtout of the rest state by the sensor signal and shifted into the activestate, an uninterrupted monitoring of the accumulator battery ispossible without significant energy being needed for that purpose.

In a particularly advantageous manner, the primary winding of atransformer is connected in the lead of the accumulator battery, itbeing very advantageous if the primary winding is formed by theaccumulator-battery lead itself. A flow of current in the lead of theaccumulator battery may thereby be detected in a simple manner.

It is particularly advantageous if the transformer is a component of acompensation (balancing)-current sensor, by which the flow of currentout of or into the accumulator battery is measured. Advantageously, fora specific embodiment of this type, almost no special outlay isnecessary for generating the activation signal of the control unit. Thishas a very favorable effect on the costs. Moreover, as a rule, almost noenergy is needed for generating the activation signal.

The indicated circuit configuration may be further improved, in that thesensor signal is initially given to a comparator.

In a simple manner, the signal emitted by the sensor may be converted bythe comparator into a signal well-suited for further processing. Since acomparator may be implemented with little expenditure and is able to beintegrated into an ASIC (application-specific IC), the costs of such aspecific embodiment are very low. However, conventional comparators withintegrated reference-voltage source, which are available on the marketas an IC, could also be used. To reliably detect a sudden currentvariation in the lead of the accumulator battery, downstream of thecomparator, a digital signal processing may be provided by which thesignal-to-noise ratio of the circuit is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a circuit configurationaccording to the present invention.

FIG. 2 shows the circuit configuration, depicted in FIG. 1, inconjunction with a compensation-current sensor.

DETAILED DESCRIPTION

As can be gathered from FIG. 1, a control unit 1 has an activation input1 a by which control unit 1 is able to be activated again from a statewith low current consumption. Control unit 1 also has two signal inputs1 b, 1 c by which the control unit is supplied with signals to beprocessed by it. In the inactive state of control-unit 1, signal inputs1 b, 1 c are highly resistive.

The circuit configuration shown in FIG. 1 also has a transformer 2having a transformer core 2 c as well as a primary winding 2 a and asecondary winding 2 b. Primary winding 2 a is disposed, for example, inlead 3 of a motor-vehicle accumulator battery.

The terminations of secondary winding 2 b are run to an amplifier 5. Theoutput of amplifier 5 is routed to signal input 4 b of a comparator 4. Avoltage corresponding to the desired operating point is applied atreference-voltage input 4 a of comparator 4. The output of comparator 4is routed to activation input 1 a of control unit 1.

If no signal is applied to activation input 1 a of control unit 1,control unit 1 goes into a state with low current consumption. In thisstate, signal inputs 1 b, 1 c are switched to be highly resistive. Thecurrent consumption of the circuit configuration is very low in thisstate.

If a current flows in line 3 to be monitored, and thus through primarywinding 2 a of transformer 2, a voltage is induced in secondary winding2 b of transformer 2. The induced voltage is amplified by amplifier 5and arrives at signal input 4 b of comparator 4. If the voltage fromamplifier 5 applied at the input 4 b of comparator 4 is greater than thevoltage applied at reference-voltage input 4 a of comparator 4,comparator 4 emits an output signal. Since the output signal ofcomparator 4 is applied to activation input 1 a of control unit 1,control unit 1 is brought from the inactive state to the active state.It is thereby able to process the signal applied at signal inputs 1 b, 1c.

The circuit configuration shown in FIG. 2 corresponds essentially to thecircuit configuration shown in FIG. 1. Identical components are providedwith the same reference numerals.

In the specific embodiment shown in FIG. 2, core 2 c of transformer 2 isformed as an annular core having an air gap. Primary winding 2 a oftransformer 2 is formed by lead 3 of a motor-vehicle accumulatorbattery. Secondary winding 2 b of transformer 2 is a coil 2 b woundabout annular core 2 c. Disposed in the air gap of annular core 2 c is asensor element 7 for detecting the magnetic field strength in the airgap of annular core 2 c. The signal outputs of sensor element 7 arerouted to signal inputs 8 a, 8 b of a first amplifier 8. Output 8 c offirst amplifier 8 is connected to coil 2 b and supplies it with currentcorresponding to the signal of sensor element 7. The current given offby first amplifier 8 is so great that the magnetic field strength in theair gap of annular core 2 is nearly zero.

The current flowing through coil 2 b causes a voltage drop U_(A) at aload resistor 6 connected in series with coil 2 b. Thus, voltage dropU_(A) is a measure for the current flowing through lead 3. To determinethe current, voltage U_(A) is given to input 1 b of a control unit 1 inwhich the current flowing through lead 3 is recorded.

The outputs of sensor element 7 are also switched to the input of asecond amplifier 5. The output of second amplifier 5 is connected tosignal input 4 b of comparator 4. At reference-voltage input 4 a ofcomparator 4, a reference voltage is applied which forms the operatingpoint of comparator 4. The output of comparator 4 is connected toactivation input 1 a of control unit 1.

If no signal is applied at activation input 1 a of control unit 1,control unit 1 is in a state with low current consumption. In thisstate, input 1 b of control unit 1 is highly resistive.

If a current flows through lead 3 of the motor-vehicle accumulatorbattery, sensor element 7 emits a voltage which is amplified by secondamplifier 5. If the voltage given off by second amplifier 5 exceeds thevoltage applied at reference-voltage input 4 a of comparator 4,comparator 4 emits a signal, whereby control unit 1 is activated. Afterthe activation of control unit 1, the signal applied at input 1 b may beprocessed in control unit 1.

If no current is flowing any longer in lead 3, no voltage is given offany longer by sensor element 7, which means the output signal ofcomparator 4 applied to activation input 1 a of control unit 1 becomeszero. Control unit 1 thereby goes into a state with low currentconsumption.

1. A circuit configuration for monitoring a state of charge of a batterysituated in a motor vehicle, the circuit configuration comprising: acontrol unit for recording and evaluating a flow of current out of orinto the battery, the control unit being adapted to be shifted into astate with low current consumption, the control unit being furtheradapted to be brought out of the state with low current consumption byan activation signal; and a sensor for emitting a signal in response toa flow of current out of or into the battery, the sensor coupled to atleast one primary winding of a transformer, the primary winding beingcoupled to a lead of the battery and being used to detect a flow ofcurrent in the lead.
 2. The circuit configuration according to claim 1,wherein the state with low current consumption is a sleep mode.
 3. Thecircuit configuration according to claim 1, wherein the primary windingis formed by the lead of the battery itself.
 4. The circuitconfiguration according to claim 3, wherein the transformer is acomponent of a compensation-current sensor, by which the flow of currentout of or into the battery is measured.
 5. The circuit configurationaccording to claim 1, further comprising a comparator for receiving thesensor signal.